From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932325Ab2JSNct (ORCPT ); Fri, 19 Oct 2012 09:32:49 -0400 Received: from cantor2.suse.de ([195.135.220.15]:54114 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752732Ab2JSNcq (ORCPT ); Fri, 19 Oct 2012 09:32:46 -0400 Date: Fri, 19 Oct 2012 15:32:45 +0200 From: Michal Hocko To: Tejun Heo Cc: linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Li Zefan , Johannes Weiner , KAMEZAWA Hiroyuki , Balbir Singh Subject: Re: [PATCH 4/6] cgroups: forbid pre_destroy callback to fail Message-ID: <20121019133244.GE799@dhcp22.suse.cz> References: <1350480648-10905-1-git-send-email-mhocko@suse.cz> <1350480648-10905-5-git-send-email-mhocko@suse.cz> <20121018224148.GR13370@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121018224148.GR13370@google.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 18-10-12 15:41:48, Tejun Heo wrote: > Hello, Michal. > > On Wed, Oct 17, 2012 at 03:30:46PM +0200, Michal Hocko wrote: > > Now that mem_cgroup_pre_destroy callback doesn't fail finally we can > > safely move on and forbit all the callbacks to fail. The last missing > > piece is moving cgroup_call_pre_destroy after cgroup_clear_css_refs so > > that css_tryget fails so no new charges for the memcg can happen. > > The callbacks are also called from within cgroup_lock to guarantee that > > no new tasks show up. We could theoretically call them outside of the > > lock but then we have to move after CGRP_REMOVED flag is set. > > > > Signed-off-by: Michal Hocko > > So, the plan is to do something like the following once memcg is > ready. > > http://thread.gmane.org/gmane.linux.kernel.containers/22559/focus=75251 > > Note that the patch is broken in a couple places but it does show the > general direction. I'd prefer if patch #3 simply makes pre_destroy() > return 0 and drop __DEPRECATED_clear_css_refs from mem_cgroup_subsys. We can still fail inn #3 without this patch becasuse there are is no guarantee that a new task is attached to the group. And I wanted to keep memcg and generic cgroup parts separated. -- Michal Hocko SUSE Labs